Since a hermetical rotational compressor is compact in size and its structure is simple, the hermetical rotational compressor is widely used for a refrigerator-freezer, air conditioners and the like. Non-patent document, [“Air-Conditioning and Refrigeration handbook”, new edition 5, volume II, machine”, Air-Conditioning and Refrigeration Institute, 1993, paragraphs 30 to 43], describes structures of hermetical rotational compressors such as a rotary compressor and a scroll compressor. A structure of the conventional hermetical rotational compressor will be explained based on the rotary compressor and the scroll compressor with reference to FIGS. 8 to 10.
FIG. 8 is a vertical sectional view of the conventional rotary compressor. The rotary compressor shown in the drawings comprises a container 1, a shaft 2 having an eccentric portion 2a, a cylinder 3, a roller 4, a vane 5, a spring 6, an upper bearing member 7 having a discharge hole 7a, a lower bearing member 8, a stator 11 having coil ends 11c and 11d projecting from upper and lower end surfaces 11a and 11b, respectively, and a rotor 12 fitted over the shaft 2.
In the above structure, a portion comprising the stator 11 and the rotor 12 is called a rotational motor, and a portion which forms a suction chamber and a compression chamber (not shown) in the cylinder 3 and which compresses a working fluid as the rotor 12 rotates is called a compression mechanism.
An outer periphery of the stator 11 is provided with a plurality of notches 11e which function as passages of the working fluid. A gap 18 is provided between the stator 11 and the rotor 12. The container 1 is provided at its upper portion with an introduction terminal 13 for energizing the rotational motor from outside of the container 1, and a discharge pipe 15 for discharging the working fluid from the container 1 into a refrigeration cycle. The container 1 is provided at its side surface with a suction pipe 14 for introducing the working fluid from the refrigeration cycle into the compression mechanism. The container 1 is provided at its bottom with an oil reservoir 16 where refrigeration oil is reserved.
The operation of the rotary compressor having the above-described structure will be explained.
If the stator 11 is energized through the introduction terminal 13 to rotate the rotor 12, the roller 4 is eccentrically rotated by the eccentric portion 2a, and volumes of the suction chamber and the compression chamber are varied. With this, the working fluid is sucked into the suction chamber from the suction pipe 14 and is compressed in the compression chamber. The compressed working fluid supplied from the oil reservoir 16 is mixed with a refrigeration oil which lubricated the compression mechanism and, in this state, the working fluid is injected into a lower space 17 of the rotational motor through the discharge hole 7a. 
The most of injected working fluid collides against a lower end surface 12a of the rotor 12 and then produces a strong turning flow by the rotation of the rotor 12. While the working fluid remains in the lower space 17 as a turning flow, a portion of the oil drops included in the working fluid attaches to an inner wall of the container 1 by a centrifugal force or drops downward due to gravity and returns into the oil reservoir 16.
In a state in which the working fluid includes the oil drops which are not separated, the most of working fluid passes through the notches 11e and the gap 18 from the lower space 17, and is injected toward an upper space 19 of the rotational motor. The injected working fluid flows toward the discharge pipe 15 but at that time, a portion of the working fluid passes in the vicinity of an upper end surface 12b of the rotor 12, and produces the turning flow due to the rotation of the rotor 12. While the working fluid stays in the upper space 19, a portion of the oil drop included in the working fluid attaches to the inner wall of the container 1 by the centrifugal force or drops downward due to the gravity and is separated, and returns into the oil reservoir 16 along the inner wall of the container 1 or a wall surface of the stator 11. The working fluid including the oil drops which are not yet separated is discharged from the discharge pipe 15.
FIG. 9 is a vertical sectional view of a conventional scroll compressor. The scroll compressor shown in FIG. 9 comprises a container 31, a shaft 32 having an eccentric portion 32a, a stationary scroll 33 having a spiral lap 33a and a discharge hole 33b, a moving scroll 34 having a spiral lap 34a and turning as the eccentric portion 32a eccentrically rotates, an upper bearing member 36 having the discharge hole 36c and supporting one end of the shaft 32, a stator 39 which has coil ends 39c and 39d projecting at right and left end surfaces 39a and 39b, respectively, and which is shrinkage fitted into the container 31, a rotor 40 shrinkage fitted over the shaft 32, and an auxiliary bearing member 41 supporting the other end of the shaft 32.
The lap 33a and the lap 34a are meshed with each other, and a plurality of suction chambers 37 and compression chambers 38 are formed in the stationary scroll 33 and the moving scroll 34. In the above structure, a structure comprising the stator 39 and the rotor 40 is called a rotational motor, and a structure which forms the suction chambers 37 and the compression chambers 38 and which compresses a working fluid as the rotational motor rotates is called a compression mechanism.
An outer periphery of the stator 39 is provided with a plurality of notches 39e which function as passages of the working fluid. A gap 48 is formed between the stator 39 and the rotor 40. The container 31 is provided with an introduction terminal 42 for energizing the rotational motor from outside of the container 31. The container 31 is also provided with a suction pipe 43 for introducing the working fluid into the suction chambers 37 from the refrigeration cycle, and a discharge pipe 44 for discharging the working fluid into the refrigeration cycle from the container 31. Refrigeration oil is reserved in an oil reservoir 45 formed in a lower portion of the container 31, and the refrigeration oil is drawn up by an oil supply pump 46 from the oil reservoir 45, and is supplied to the compression mechanism.
The operation of the scroll compressor having the above-described structure will be explained.
If the stator 39 is energized through the introduction terminal 42 to rotate the rotor 40, the moving scroll 34 turns, and volumes of the suction chambers 37 and the compression chambers 38 are varied. With this, the working fluid is sucked from the suction pipe 43 into the suction chambers 37, and is compressed in the compression chambers 38. The compressed working fluid is supplied from the oil reservoir 45, and is mixed with oil drops of the refrigeration oil which lubricated a sliding surface of the compression mechanism and, in this state, the working fluid is injected into a right space 47 of the rotational motor through the discharge holes 33b and 36c. 
The most of injected working fluid produces a turning flow by rotation of a right end surface 40a of the rotor 39. While the working fluid stays in the right space 47 as the turning flow, a portion of the oil drops included in the working fluid attach to the inner wall of the container 1 by the centrifugal force or drop due to the gravity, and is separated from the working fluid and returns into the oil reservoir 45.
In a state in which the working fluid includes oil drops which are not yet separated, the working fluid passes through the notches 39e or the gap 48 from the right space 47, and is injected into a left space 49 of the rotational motor. The most of injected working fluid flows toward the discharge pipe 44 but at that time, a portion of the working fluid passes in the vicinity of a left end surface 40b of the rotor 40, and produces a turning flow due to rotation of the rotor 40. While the working fluid remains in the left space 49, a portion of the oil drops included in the working fluid attaches to the inner wall of the container 1 by the centrifugal force or drops downward due to gravity and is separated and returns into the oil reservoir 45. The working fluid including the oil drops which are not yet separated is discharged from the discharge pipe 44.
In the hermetical type compressor such as the rotary compressor and the scroll compressor, in order to lubricate the sliding surface of the compression mechanism and to seal the gap, the compressed working fluid and refrigeration oil are mixed, a portion of the refrigeration oil reserved in the oil reservoir is discharged out from the container 1, 31 of the compressor in the course of operation of the compressor, but in the case of a compressor having a high amount of discharged refrigeration oil, since the oil level of the refrigeration oil in the oil reservoir 16, 45 is lowered, the supply oil amount becomes insufficient, and the lubrication of the compression mechanism becomes insufficient, the reliability is deteriorated, the sealing of the compression mechanism becomes insufficient, and the efficiency of the compressor is deteriorated. Further, the refrigeration oil discharged from the compressor attaches to an inner wall of a tube of a heat exchanger to deteriorate the heat transfer coefficient between the working fluid and a wall surface in the heat exchanger tube. Thus, the performance of the refrigeration cycle is deteriorated. Therefore, the oil separating efficiency of the working fluid in the container 1, 31 of the compressor is enhanced, and the discharging amount of the refrigeration oil is reduced.
As a structure for separating the refrigeration oil from the working fluid, there is a method to use an oil separating plate provided on an upper portion of the rotor 12 of the rotary compressor as shown in a patent document, [Japanese Patent Application Laid-open No.H8-28476 (paragraph 6, FIGS. 1 to 3)] FIG. 10 shows a detailed sectional view of a periphery of the oil separating plate. The rotor 12 has an upper end plate 21a and a lower end plate 21b for closing inserting holes of a permanent magnet 20. A plurality of through holes 12c formed in the rotor 12 are provided to penetrate the rotor 12 in the vertical direction, and an oil separating plate 23 which is disposed above exits of the through holes 12c and which forms an oil separating space 22 between itself and an upper end surface of the rotor 12 are fixed to the rotor 12 by a fixing member 24.
According to the compressor having such a structure, a portion of the working fluid including oil drops discharged into the lower space 17 of the rotational motor from the compression mechanism flows into the oil separating space 22 through the through holes 12c formed in the rotor 12. The working fluid is radially discharged from the outer peripheral exit of the oil separating plate 23, and blows against the coil end 11d of the stator 11, and separates the refrigeration oil included in the working fluid. Only the working fluid from which the refrigeration oil is separated flows upward, and is discharged out from the discharge pipe 15 provided on the upper portion in the container 1. On the other hand, refrigeration oil attached to the coil end 11d of the stator 11 drops downward and returns into the oil reservoir 16 formed in the bottom of the container 1.
As described above, in the conventional rotary compressor, the most of working fluid injected into the lower space 17 of the rotational motor from the discharge hole 7a of the compression mechanism produces the strong turning flow by rotation of the rotor 12. The working fluid injected into the upper space 19 also produces the turning flow due to the rotation of the rotor 12. Similarly, the most of working fluid injected into the right space 47 and the left space 49 of the scroll compressor produces the turning flow due to the rotation of the rotor 40.
At that time, the oil drops of the refrigeration oil included in the working fluid are stirred by the turning flow and are finely divided. Since the turning flow in the lower space 17, the upper space 19, the right space 47 and the left space 49 increases the flow speed of the working fluid, the oil drops are prone to be transported by the working fluid. Therefore, it is difficult to completely separate the refrigeration oil from the working fluid by the separating method by means of the centrifugal force and gravity. Each of the lower end surface 12a and the upper end surface 12b of the rotor 12 is provided with a balancer 12d for overcoming the unbalance state of the roller 4 and the eccentric portion 2a of the shaft 2. Similarly, each of the right end surface 40a and the left end surface 40b of the rotor 40 is provided with a balancer 40c. In the case of a brushless DC motor, a bolt or a rivet (not shown) is provided for fixing a laminated steel plate and the magnet forming the rotor. As a result, the end surface of the rotor is formed with a large number of asperities, and the stirring of the working fluid is enhanced by rotating the asperities. Therefore, the oil drops of the refrigeration oil included in the working fluid are divided more finely, and it becomes difficult to separate the refrigeration oil from the working fluid.
As a method for separating the stirred and finely divided oil drops from the working fluid, the structure shown in FIG. 10 is used. In this case, however, with regard to the working fluid flowing from the lower space 17 toward the upper space 19 of the rotational motor, this method is effective only for the working fluid passing through the through holes 12c formed in the rotor 12, and it is impossible to separate the oil drops from the working fluid passing through the notches 11e of the stator 11 and the gap 18 between the stator 11 and the rotor 12. Further, the oil separating plate 23 is provided on the upper end surface 12b of the rotor. This structure promotes the stirring of the working fluid in the upper space 19 of the rotational motor, and there is a problem that it is more difficult to separate the refrigeration oil in the upper space 19.
As another method, volumes of the lower space 17 and the upper space 19 of the rotational motor are increased, and a time during which the working fluid stays in such spaces is lengthened, and separation of the oil drop of the refrigeration oil is promoted by the gravity. However, in this case also, it is difficult to eliminate the influence of the stirring, and there is another problem that the compressor is increased in size.
The above description is based on the vertical type rotary compressor or the lateral type scroll compressor, but if the working fluid passes through an end surface of the rotor while a refrigerant discharged from the compression mechanism is discharged from the discharge pipe provided on the container, irrespective of a difference between the vertical type and the lateral type or irrespective of a difference of the compressing manners, the same problems mentioned above exist.
The above problems are generated irrespective of kinds of the working fluid which are used. However, the problems are particularly severe when the refrigeration cycle uses a working fluid mainly comprising carbon dioxide as a main ingredient, since the pressure of the working fluid discharged from the compression chamber exceeds a critical pressure, the working fluid in the container is brought into a supercritical state, and an amount of refrigeration oil solved in the working fluid is increased, thereby making it more difficult to separate the oil in the container.
The present invention has been accomplished to solve the above problems, and it is an object of the invention to provide a compressor capable of easily and inexpensively enhancing the oil separating efficiency without deteriorating the efficiency of the rotational motor, capable of reducing the amount of refrigeration oil to be removed from the container, and capable of enhancing the reliability of the compressor and obtaining an efficient refrigeration cycle.
As described above, according to the present invention, porous members are provided in the space between the rotational motor and the compression mechanism and the space between the rotational motor and the discharge pipe and the spaces are defined. Thus, the stirring phenomenon by turning flow caused due to rotation of the rotor and the stirring phenomenon caused by rotation of the asperities such as the balancer provided on the end surface of the rotor can be pushed into the space on the side of the rotational motor defined by the porous member so that the oil drops of the refrigeration oil mixed in the working fluid are prevented from being divided finely by the stirring phenomenon.
With this the effect that the oil drops falls due to the gravity and are separated is promoted, and the oil separating efficiency can be enhanced, and reliability and efficiency of the compressor and the refrigeration cycle using the compressor can be enhanced.